Current sensor and short circuiting means therefor



Jan. 28, 1969 e. G. SCHOCKELT 3,425,017

CURRENT SENSOR AND SHORT CIRCUITING MEANS THEREFOR Original Filed Juneso, 1966 j I j /3.2

05 04 w m M M15 7 49/415 440 Q 63 /60 j M WM /55 62 /57 j I A I I l- 7 vg 6016/ A56 A37 /59 H6? m2 m 0/ 2 W5 United States Patent 7 ClaimsABSTRACT OF THE DISCLOSURE A current sensor having contacts bridged by afusible element operates on predetermined current flow to close thesecontacts and perform a mechanical control function.

This application is a division of application Ser. No. 561,839, filedJune 30, 1966.

This invention relates to metal enclosed switchgear for application toalternating current circuits operating at voltages of the order of 13.2kv. It can be employed for circuits operating at higher -or lowervoltages and for different current ranges as may be required. Itconstitutes an improvement over the constructions disclosed in US. Beebeet al. Patent 3,055,996, issued Sept. 25, 1962, and in copendingapplications Ser. No. 552,282, filed May 23, 1966, and Ser. No. 561,839filed June 30, 1966.

For electric power distribution at various locations, such as shoppingcenters, high rise buildings, industrial plants, etc., and at relativelyhigh voltage, for example 13.2 kv., switching equipment is provided thatmust be reliable and safe. Such equipment is arranged for normalsupervision and operation by personnel of limited skill whosecapabilities extend only to routine operations involving opening andclosing a circuit, changing blown current responsive means, such as fusedevices, etc. Because of competitive conditions, the cost of thisswitching apparatus is required to be held to a minimum consistent withproper and safe operation.

Among the objects of this invention are: To employ a current sensor withfusible means capable of carrying full load current continuously andarranged to blow on flow of excess current therethrough in accordancewith the time-current characteristic of a fuse to release an operatingmember for opening a current interrupter; and to shunt the blown fusiblemeans to maintain circuit continuity with respect only to the blownfusible means to permit opening of the circuit by the circuitinterrupter.

In the drawing: FIG. 1 is a longitudinal sectional view, at an enlargedscale, of the current sensor. FIG. 2 is a vertical sectional view, takengenerally along the line 2-2 of FIG. 1. FIG. 3 is a View in endelevation, looking from right to left, of the terminal member employedin the current sensor shown in FIG. 1. FIG. 4 is a view at a reducedscale and somewhat similar to FIG. 1 to show the current sensor in theoperated condition.

In FIG. 1 a current sensor is indicated, generally, at 40 and it isarranged to be connected in series circuit relation with a switch bladeand a current interrupter as disclosed in the application of which thisapplication is a division. The current sensor 40' is mounted on aplatelike lower end 74 of a conductor that forms a part of the seriescircuit to the current interrupter and switch blade. The current sensor40 is mounted directly on an upper contact plate 75 which has a plate 76of insulation between it and the plate-like lower end 74 of theconductor. It will be observed that the conductor plates 74 and 75, withthe insulating plate 76 therebetween, are

3,425,017 Patented Jan. 28, 1969 held together by flat head screws 131which extend through insulating bushings 132 in the conductor plate 74.An internally threaded metallic guide bushing 133, preferably formed ofcopper, is secured to the upper contact plate and has threaded thereinone end of a tubular metallic housing 134 that also is formed preferablyof copper. At its distal end the tubular metallic housing 134 isprovided with a cap 135 of copper and it has an inwardly extendingannular contact portion 136 that is arranged to be engaged, in a mannerto be described, by contact fingers 137, FIG. 2, which extend from acontact tube 138 that preferably is formed of copper and makes contactwith the conductor plate 74. An insulating sleeve 139 serves to spacethe tubular metallic housing 134 from the contact tube 138.

In order to insulate normally the annular contact portion 136 from thecontact fingers 137, an internal layer of insulation 140* is formed atone end of a metallic tension tube 141 which is slidably mounted withinthe contact tube 138: and extends outwardly therefrom. The metallictension tube could be formed wholly of insulation. However, in order toprovide the requisite strength within the limited confines of thecontact tube 138, it has been found desirable to employ the metallictension tube 141, preferably formed of steel, with the internal layer ofinsulation 140 in the manner described. Slotted openings 142 are locatedin diametrically opposite sides of the tension tube 141 and at the endopposite the layer of insulation 140. The inner ends of the slottedopenings 142 form shoulders 143, FIG. 4, that are arranged to engageinner sides 144 of an end portion 145 of a terminal member 146, FIG. 3,which has a press fit with the outer end of the contact tube 138. Theterminal member 146 preferably is formed of copper. The tension tube 141extends past the end portion 145 of the terminal member 146 and throughan opening 147 in the conductor plate 74. Its outer end is closed by ametallic end plug 148 that may be formed of aluminum. A coil compressionspring 149 reacts between a shoulder 150 and the end surface of the endportion 145 for normally biasing the tension tube 141 outwardly.

In order to restrain the outward movement of the tension tube 141 asurged by coil compression spring 149, fusible means, shown generally at152, are employed. Under normal operating conditions the fusible means152 shunts the contact portion 135 and the contact fingers 137 extendingfrom the contact tube 138. The fusible means 152 includes a fusibleelement 153 which may be a coil of silver wire. One end of the fusibleelement 153' is secured to the inner end of a terminal member 154,preferably in the form of a copper rod, which extends through the cap135 and contact portion 136 and is secured thereto by a set screw 155.The other end of the fusible element 153 is secured to a hexagonal head156 of a fuse element fitting, shown generally at 157', which isthreaded at 158 into the adjacent end of a stem 159 which forms a partof the terminal member 146. The fusible means 152 also includes a strainelement 160, preferably in the form of nichrome wire, with one end beingsecured to the terminal member 154 and the other end extending throughthe fitting 157 and through the terminal member 146. The outer end ofthe strain element 160 extends through the metallic end plug 148 and issecured thereto by a set screw 161. Extending outwardly from the endplug 148 is a quick detachable fitting 162 the purpose of which will bedescribed presently.

Normally the current path from the conductor plate 75 to the conductorplate '74 is as indicated by the line with arrow heads and extendsthrough the metallic guide bushing 133, tubular metallic housing 134,cap 135, terminal member 154, fusible means 152, fuse element fitting1'57, terminal member 146, and contact tube 13-8 to the conductor plate74. The fusible means 152 are arranged and constructed to carry thenormal current flow of the circuit in which the current sensor 40 isconnected and also to withstand the flow of overload current inaccordance with conventional fuse practice. The timeourrentcharacteristic for the fusible means 152 is selected in accordance withthe circuit requirements. When the current flow exceeds the rating ofthe current sensor 40', the fusible element 153 melts and the entirecurrent flow then is transferred to the strain element 160 whichpromptly melts and releases the end plug 148 for movement outwardly tothe position shown by broken lines in FIG. 1 under the influence of thecoil compression spring 149. This is accompanied by endwise movement ofthe tension tube 141 and by withdrawal of the layer of insulation 140from between the annular contact portion 135 and the adjacent ends ofthe contact fingers 137. Their inherent resiliency is sufficient to movethem into contact engagement with the contact portion 136, aided by themagnetic forces generated by current flow in the closely adjacenthousing 134 and contact fingers 137, with the result that the gap formedby blowing of the fusible means 152 is promptly shunted. The reason forthis shunting arrangement is that the current sensor 40 is not intendedto have any current interrupting capacity. The current flow then, asshown by the broken line in FIG. 12, is transferred to flow directlyfrom the conductor plate 75' through the metallic housing 134 and thecontact fingers 137 of the contact tube 138 to the conductor plate 74.Here the tension tube 141 is moved to its outermost position as limitedby engagement of the shoulders 143 with the inner sides 144 of the endportion 145.

Instead of providing the layer of insulation 140 on the inside ofmetallic tension tube 141, the outer surface of the contact portion 136:can be coated with a suitable insulating material which can be readilypunctured when the voltage resulting from the blowing of the fusiblemeans 152 is applied between the contact portion 135 and the contactfingers 13-7. However, the tension tube 141 still is employed, althoughnot of the same length, to provide a member that moves from one positionto another as a result of blowing of the fusible means 152.

As described in the application of which this application is a division,the outward movement of the tension tube 141 accompanied bycorresponding movement of the quick detachable fitting 162 is employedto trip a spring biased linkage which is arranged to open the circuitinterrupter and thereafter move the series connected switch blade to theopen circuit position.

What is claimed as new is:

1. Current responsive means for controlling a circuit interrupterconnected in series therewith comprising:

fusible means for connection in series with said circuit interrupter, 1operating means biased for movement from one position to anotherposition for opening said circuit interrupter and restrained by saidfusible means, contact means arranged to shunt said fusible means onblowing thereof,

means biasing said contact means toward contact engagement, and

insulating means biased for movement from a position holding saidcontact means in said open position to another position permittingclosure of said contact means, said insulating means being restrained by5 said fusible means.

2. Current responsive means comprising:

first and second conductor means,

means holding said first and second conductor means in insulated spacedrelation,

a tubular metallic housing connected at one end to said first conductormeans and extending laterally therefrom,

contact means carried by said tubular metallic housing at its distal endand extending inwardly thereof, contact tube connected at one end tosaid second conductor means, telescoped within said tubular metallichousing, and having a plurality of contact fingers biased toward contactengagement with said contact means,

fusible means interconnecting said contact means and said contact tubeand providing a path along which current normally flows therebetween,and

insulating means interposed between said contact means and said contactfingers and arranged to be removed on blowing of said fusible meanswhereby the current flow is shifted from said path to another paththrough said contact means and said contact fingers.

3. Current responsive means according to claim 2 30 wherein:

said insulating means at least forms a part of a tubular membertelescoped with said contact tube and movable endwise thereof,

a spring biases said tubular member in a direction to remove saidinsulating means from between said contact means and said contactfingers, and means responsive to blowing of said fusible means restrainssaid tubular member. 4. Current responsive means according to claim 3wherein:

said first and second conductor means are in the form of metallic platesin overlying relation, and said means holding them in insulated spacedrelation includes a plate of insulation interposed therebetween.References Cited UNITED STATES PATENTS 974,109 10/1910 Auel et al 200ll6BERNARD A. GILHEANY, Primary Examiner.

HAROLD BROOME, Assistant Examiner.

US. Cl. X.R. 337-221

